IGCSE Physics4.5 .EM Induction

Presented to you by: YUAN JING

What is EM Induction?

It is the process of generating voltage from motion.

In other words, a changing magnetic field causes a potential difference (voltage) in a conductor causes EM Induction.

How to produce EM Induction?

When we move a wire across the magnetic field lines cutting the field lines, a small Electromotive Force-EMF (voltage) is produced. If it’s a complete circuit, a small current will flow which can be measured by using a Galvanometer*.

*A device used to measure small amounts of electric current.

An Example:

In this picture an ammeter is connected in the circuit of a conducting loop. When the bar magnet is moved closer to, or farther from, the loop, an electromotive force (EMF) is induced in the loop. The ammeter indicates currents in different directions depending on the relative motion of magnet and loop. Notice that, when the magnet stops moving, the current returns to zero as indicated by the ammeter.

Another picture of EM Induction:

A magnet is moved in and out of a coil connected to a galvanometer

Induction Coils and Other Things

A) Resistance VS Temperature Apparatus B) Induction Coils C) Crookes Tubes D) Tesla Coil

The induced current caused by moving a coil (or a magnet) in a magnetic field is increased by: moving the coil more quickly using a stronger magnet

To increase the potential difference across a coil or the current flowing through it, we must: use a stronger magnet move the magnet more quickly

increase the windings on the coil

Points to remember:

Faraday's law: The induced current is directly proportional to the speed with which the conductor cuts the magnetic field.

Fleming's right-hand rule: This rule determines the direction of the current.

Lenz's law: The induced current flows in such a direction that the magnetic effect it produces will oppose the inducing action.

Transformers: Making the magnet stronger and weaker will also

produce a changing magnetic field. You can do this by changing the current in an electromagnet (the primary coil). If another coil of wire (the secondary coil) is within the magnetic field of the primary coil, the changing magnetic field will go past the secondary coil and induce a current.

Formula: V across primary coil/V across secondary coil = # of turns in primary coil/# of turns in secondary coil

Vp/Vs=Np/Ns

Picture of a transformer: http://www.windows.ucar.edu/spaceweather/images/transformer.jpg

Generators: Generators induce a current by moving a magnet

inside a coil of wire, or by moving a coil of wire inside a magnetic field. One example of a generator is a bicycle dynamo.

Bicycles sometimes have dynamos which rub against the back tyre. As the bike moves, a wheel on the top of the dynamo turns a magnet inside a coil.

Picture of a real generator: http://www.turbinetechnologies.com/generator.jpg